Padre's Splash screen should not get in the way

Description

The current Padre splash screen does not hide itself when Padre's UI is ready delaying actual usage for like 1-2 secs on fast computers. We should kill or hide it when Padre's UI is ready to improve responsiveness.

One more thing, the splash screen sometimes appears for a while on win32 when switching through document tabs. Once it appears for the first time, the functionality should be disabled. This only happens when using padre.bat